The present invention relates to a process for increasing or decreasing the valence number of an ion in a solution, and an apparatus therefor. The invention can be employed, for example, for converting a ferrous ion into a corresponding ferric ion and an uranyl ion into a corresponding uranous ion.
The present invention also relates to a process for obtaining a ferric salt and a hydrogen gas by electrolyzing a ferrous salt solution.
Conversion of the valence number of an ion in an aqueous solution has been heretofore carried out by a method of reacting the ion with an oxidizing agent or a reducing agent, or by a method of oxidizing or reducing the ion on an anode or on a cathode by means of electrolysis.
The method of reacting with the oxidizing agent or the reducing agent has the drawback that the oxidizing agent or the reducing agent added remains in the aqueous solution after the chemical reaction. The method of electrolyzing has the drawback that an anode chamber and a cathode chamber have to be separated by an ion exchange membrane.
The separation by means of the ion exchange membrane is necessary because the ion, for example, reduced on the cathode is oxidized on the anode to return its initial state.
Another method which consists of directly bubbling an oxidizing gas or a reducing gas into the aqueous solution is known, and is employed, for example, oxidizing a ferrous ion to a ferric ion with blowing a chlorine gas into the ferrous chloride solution while heating the solution at 60.degree. to 70.degree. C., but the reaction efficiency of this method is insufficient and the method is not economical.
The present invention in particular, addresses a process for preparing a ferric chloride solution from a ferrous chloride solution by means of electrolysis. Oxidation can be easily performed employing a gas permeable electrode at the hydrogen evolving side and a titanium electrode coated with platinum or a carbon electrode at the counter electrode side. Even if the voltage is increased for promoting oxidation, electrolysis efficiency is elevated without a rise in the bath voltage because the gas permeable electrode is employed as the hydrogen evolving electrode. Moreover, the hydrogen gas is easily discharged. The applications can thus be broadened utilizing the characteristics of the ferric chloride solution.
One useful example thereof is a process for contacting ferric chloride solution which is employed with poisonous hydrogen sulfide gas in a petroleum refining plant. A solution containing ferrous chloride and hydrogen chloride after the filtration of sulfur can be circulated and utilized by converting the ferrous chloride and the hydrogen chloride into ferric chloride and hydrogen according to the present invention.